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Hydrodynamics of Microalgae and Co2 Flow in a Tubular Photobioreactor and Consequent Effects on Microalgae Growth

Saumen Barua
Department of Mathematics, Sir Ashutosh Govt. College, Chittagong, Bangladesh.

Ujjwal Kumar Deb
Department of Mathematics, Chittagong University of Engineering & Technology, Chittagong, Bangladesh.

Abstract/ Executive Summary:

In biofuel technology from microalgae, the main optimal factors for microalgae cultivations are light, CO₂ and temperature. As microalgae are photosynthetic microorganisms thus they convert sunlight, water and CO₂ to algal biomass. We consider a two phase flow for CO₂ and Microalgae suspension to understand fluid dynamics phenomena after injecting CO₂ gas inside a tubular Photobioreactor (PBR).The growth rate of the microalgae cell is taken as a function of available sun light at Chittagong University of Engineering & Technology (CUET) in our study. A 20.94m long and 0.025m tubular PBR is considered for the simulation. To observe the microalgae cell growth, we selected the 21st June for a bright sunny and the longest day of a year. From the simulation after day seven we observed a very slow growth for the microalgae culture. It is noted that the growth related to concentration of microalgae is increased by day length with respect to continuous sunlight. A small fluctuation of shear rate around Uloop area is also found in our simulation which may be caused to reduce the volumetric production due to cell fragility. From the velocity profile we found that, the velocity is generally higher in the middle of the tube gives a parabolic shape of the suspension flow.

Keywords: Microalgae, Biofuel, Tubular Reactor, CFD, Simulation.

Location: Department of Mathematics, Sir Ashutosh Govt. College, Chittagong, Bangladesh.

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Algae

Objectives:

In this study, a two phase flow, which means to understand fluid dynamics phenomena after injecting the CO₂ gas in the tubular PBR together with microalgae suspension, is investigated. The consequent effects on the cell concentration due to the sunlight at CUET and some fluid dynamics phenomena including Share rate, Pressure and velocity profile are also investigated.

Methodology:

MATHEMATICAL MODEL In this study, an airlift driven horizontal loop tubular photobioreactor is considered. A uniform mixture of microalgae suspension and CO₂ were injected inside the tubular photobioreactor. This mixture is considered as an incompressible two phase Newtonian fluid and the flow problem is assumed to be laminar in our simulation. I COMPUTATIONAL DOMAIN AND MESH DESIGN The photobioreactor considered in our study with radius of 0.025 m and length of 20.94m. The surface area and volume of the photobioreactor are 3.279 m²and 0.04043 m³ respectively. A coarse mesh design is considered for our simulation with 1, 25,691 elements and 10, 55,747 degrees of freedom. GOVERNING EQUATIONS We consider the mixture between the microalgae suspension and CO₂ is uniform thus a two phase flow model for the mixture is reckoned which is incompressible Newtonian fluid. We also consider the flow problem is laminar. BOUNDARY AND INITIAL CONDITIONS In this simulation the inlet initial velocity for CO₂ is 0.5ms^-1 and the fluid flow is uniform. The volume frictions of CO₂ and microalgae suspension are 0.05 and 0.95. Also we considered no-slip boundary condition on the wall i.e. 0 =u r and zero normal stress at the outlet of the domain.

Source of Information: Rajshahi University Journal of Science & Engineering ISSN 2309-0952 Vol. 44: 75-83, 2016

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In our study, a two phase flow model for microalgae suspension and CO₂ is considered to understand the flow dynamics inside a photobioreactor and the concomitant essence on microalgae cell growth. The growth rate of the microalgae cell is taken as a function of solar irradiance at CUET in our study. From our study we observe that, a general parabolic shape of velocity profile is found at different cross-sections inside the tubular photobioreactor. A very slow growth of microalgae is found due to light irradiance after the day seven for the microalgae culture in our simulation. In case of shear rate distributions we found irregular shape around U-loop area while it is regular for straight part of the computational domain.

Knowledge Management: Journal